Preeclampsia is a disease characterized by new onset of hypertension and proteinuria during the second half of pregnancy, affecting 3-8% of pregnancies. It is a leading cause of maternal and fetal morbidity and mortality, and delivery remains the only known treatment.!Fine particulate matter (PM2.5) air pollution has been persuasively linked to increased risk of cardiovascular morbidity and mortality, with pollution from traffic identified as a key source. Maternal exposure to air pollution may also be associated with slower fetal growth, lower birth weight, and higher risk of preterm birth and small size for gestational age at birth. Preeclampsia is one of the leading causes of preterm birth and small size for gestational age, and thus may be an early event leading to these outcomes. However, few studies have evaluated the association between air pollution and risk of preeclampsia. To rigorously address this hypothesis, we propose a novel two-pronged approach consisting of: 1) a large cohort study based on detailed administrative and vital records data on 88,000 singleton births between 2002 and 2011 at the Women and Infants Hospital of Rhode Island, including >4,000 patients with a discharge diagnosis of preeclampsia, and 2) a large, case-control study (1000 cases/1000 controls) nested within this cohort with detailed review of medical records from prenatal care to delivery to obtain, for the first time, data on: a) maternal residential histry throughout the pregnancy, and b) clinical features and timing of onset of preeclampsia. In both studies we will estimate residential exposure to PM2.5 throughout pregnancy using a novel, high-resolution (1 km grid) spatial-temporal model informed by both satellite and ground based monitoring, and residential exposure to pollution derived from traffic sources by extending our validated spatial-temporal model of black carbon. Thus, the proposed project combines the strongest features of previous studies and offers novel refinements. Given ubiquitous exposure to ambient air pollution, the public health importance of preeclampsia, suggestive preliminary epidemiologic evidence, and the biologic plausibility of a link between exposure and preeclampsia, this hypothesis warrants further evaluation with improved methods for assessing exposures, health outcomes, and their interrelationships.